The present invention relates to deflection-compensation of rolls of the type which are used in the manufacture of paper.
In particular, the present invention relates to deflection-compensation of calendar rolls, especially filled calendar rolls of the type used in supercalenders.
As is well known, supercalenders are utilized in the manufacture of paper for the purpose of burnishing the paper web. Such supercalenders conventionally include a number of hard rolls and also may include a number of soft rolls equal to the number of hard rolls, these soft rolls being paper-coated rolls, commonly referred to as filled rolls, and these latter filled rolls cooperate with the hard rolls. The filled rolls, as is well known, may be made of a material possessing resilient or elastic properties. The filling of the filled rolls is obtained by compressing fabrics, papers, or nonwoven mats of cellulose fiber under high pressure.
One of the features disclosed in the above application is a calendar arrangement which includes a stack of hard rolls situated one above the other and defining hard nips between themselves, this stack including upper and lower rolls and a pair of intermediate rolls engaging the upper and lower rolls, with these intermediate rolls being in turning engaged by the soft or filled rolls of which there are at least two forming a pair of soft nips with the intermediate rolls.
In a calender arrangement of this latter type particular problems are encountered. Thus, a plane which contains the axis of one of the above filled rolls and the nip between this filled roll and a hard roll is not situated vertically. In addition, the load of the filled rolls is adjustable. As a result of these circumstances, the direction of the resultant of the weight of the filled roll and the direction in which the pressure acts at the nip is subject to change as the loading at the nip is changed. Therefore, the control of the deflection of the calender rolls and the control of the distribution of the line pressure at the nip defined between the filled rolls and hard rolls becomes difficult and complicated.